In devices having rotary shafts, particularly in adjustable position impeller pumps, it is sometimes desirable to adjust the position of the impeller in the pump by adjusting the position of the shaft upon which the impeller is mounted. Typically, the shaft seals of such pumps include a drive ring attached to the shaft by means of a set screw or other similar fastener. The drive ring provides a base for a mating ring, which forms the rotating portion of the shaft seal. The stationary portion of the shaft seal is secured to the bearing housing. In such an arrangement, positional adjustment of the shaft requires several steps, including partial disassembly of the housing to gain access to the set screw on the drive ring, repositioning and resquaring of the drive ring, resetting the sealing force of the stationary seal member, and reassembly of the housing. Great care must be taken to ensure precise adjustment of the shaft seal, since improper seating of the seal members could result in undue wear and premature failure of the seal. As is apparent from the foregoing description, adjustment of previously known shaft seals is cumbersome, time-consuming and expensive.